Tetrahedral boron chemistry for the preparation of highly efficient "cascatelle" devices

The replacement of the two fluorine atoms on the boron center of the well-known Bodipy fluorophore by functionalized acetylenic groups opens the way to a new family of highly luminescent, redox active, and stable fluorophores termed "E-Bodipy" species. The substitution is effective for ethynyl-lithium reagents incorporating tolyl, naphthyl, pyrenyl, fluorenyl, and terpyridinyl units. The protocol also tolerates the presence of various functional groups in the dipyrromethene meso position such as pyrene, phenylethynylpyrene, 4'-terpyridine, and iodophenyl. The last of these is particularly useful for a further coupling reaction enabling introduction of a flexible arm bearing a succinimidyl unit reactive toward primary amines. X-ray structure determinations of two E-Bodipy compounds confirm the introduction of the ethynyl units and show the boron atoms to have a distorted tetrahedral environment, with B-C(ethynyl) approximately 1.59 A and both boron atoms lying essentially in the mean planes of the dipyrromethene units. All the new compounds show intense electronic absorption bands (epsilon 60,000-70,000 M-1 cm-1), high quantum yields (>80%), and slow rates of nonradiative decay. Absorption by the aromatic substituents results in a "cascatelle" process leading to emission exclusively through the boradiazaindacene entity and thus large virtual Stokes' shift (>10,000 cm-1). The new compounds are also redox active, with the formation of both Bodipy+* and Bodipy-* occurring more readily than for F-Bodipy species. The molecules in their excited states are strong reducing agents.     

Extrapolation methods for approximating arc length and surface area

A well-known method of estimating the length of a parametric curve in is to sample some points from it and compute the length of the polygon passing through them. In this paper we show that for uniform sampling of regular smooth curves, Richardson extrapolation can be applied repeatedly giving a sequence of derivative-free length estimates of arbitrarily high orders of accuracy. A similar result is derived for the approximation of the area of parametric surfaces.      

Infrared-laser-pulse control of bond- and state-selective excitation, dissociation and space quantization: application to a three-dimensional model of HONO2 in the ground electronic state

Selective control over the vibrational excitation and space quantization of the dissociation fragments by optimally designed linearly polarized and shaped infrared (IR) laser pulses of the picosecond (ps) and subpicosecond duration is demonstrated by means of quantum-dynamical simulations within the Schr?dinger wave-function formalism for a three-dimensional (3-D) model of HONO₂ in the ground electronic state, wherein the OH and the ON single-bond stretches are explicitly treated, together with the bending angle between them, on the basis of the ab initio defined 3-D potential-energy surface and dipole function. The high-lying zeroth-order vibrational states of the OH bond are prepared selectively both below and above the dissociation threshold of the ON single bond, and demonstrate a quasi-periodic oscillatory behaviour, manifesting intramolecular vibrational energy redistribution (IVR) on the picosecond timescale. Selective breakage of the ON single bond in HONO₂ with more than 97% probability is demonstrated, along with control of the space quantization of the dissociation fragments: the OH fragments rotating clockwise, OH(c), and anticlockwise, OH(a), are prepared selectively, with the OH(a)/OH(c) branching ratio being as high as 10.975. The results obtained show that optimally designed strong and short IR-laser pulses can compete against IVR and manipulate vibrational excitation and dissociation of polyatomic molecules. Received: 3 November 1999 / Published online: 13 July 2000     

Polystyrene with Pendant Mixed Functional Ruthenium(II)‐Terpyridine Complexes

A vinyl substituted 2,2′:6′,2″‐terpyridine and a mixed, bifunctional ruthenium(II)‐terpyridine complex bearing a vinyl and a hydroxymethyl group are utilized as comonomers for radical copolymerization with styrene. The resulting polymers are characterized by means of UV‐vis spectroscopy and gel permeation chromatography, coupled with an in‐line diode array spectrophotometer.     

Calcium Thiolates and Selenolates: Synthesis and Structures

The synthesis and structural characterization of a family of calcium thiolates and selenolates is described. In the solid state the compounds adopt either contact pairs, as observed in Ca(THF)₄(SMes*)₂ ( 1 ), (Mes* 2,4,6‐tBu₃C₆H₂), and Ca(THF)₄(SeMes*)₂, ( 2 ), or separated ions as shown in [Ca(18‐crown‐6)(HMPA)₂][SeMes*]₂ ( 3 ). The two different ion association modes are induced by addition of specific donors. The compounds were prepared by metalation involving the reaction of elemental calcium dissolved in dry liquid ammonia with either HSMes* or Mes*SeSeMes*. All compounds were characterized by X‐ray crystallography, NMR and IR spectroscopy.